1. Field of the Invention
The present invention relates to an exhaust assembly for a construction machine, which is provided with an exhaust pipe for releasing engine exhaust gas, which has been discharged from an after-treatment device for the engine exhaust gas, to the outside.
2. Description of the Related Art
In general, a construction machine such as a hydraulic excavator is provided with a travel base having crawler tacks or the like to travel, a revolving upperstructure connected to an upper part of the travel base via a revolving frame and swingable in a horizontal direction, and a front working mechanism arranged on a front section of the revolving upperstructure and having actuators to perform work such as digging.
The revolving upperstructure of the construction machine is in turn provided with an engine accommodated inside an engine compartment, an after-treatment device for treating exhaust gas from the engine, and an exhaust pipe for releasing the exhaust gas, which has been guided from an outlet port of the after-treatment device, to the outside.
As one of conventional technologies on after-treatment devices arranged in such construction machines, an after-treatment device for use in a diesel engine is known. This after-treatment device is provided with an exhaust choke valve arranged on a downstream side, and is adapted to increase the temperature of exhaust gas such that catalytic activity is assured, and is intended to reduce noise which is produced upon opening of the exhaust choke valve (see, for example, JP-A-2005-282533).
In the above-mentioned exhaust gas after-treatment device for the diesel engine as disclosed in JP-A-2005-282533, an oxidation catalyst is employed as a catalyst for removing particulate matter such as hydrocarbons. As a result of an oxidative reaction of the particulate matter on the oxidation catalyst, water vapor is produced. In an exhaust assembly for a construction machine, said exhaust assembly being provided with such an after-treatment device, water vapor is discharged into an exhaust pipe together with exhaust gas guided from the after-treatment device. When the temperature of the exhaust pipe is low, the water vapor is cooled in the exhaust pipe so that water droplets condense and adhere on an inner wall of the exhaust pipe. The condensation and adhesion of water droplets on the inner wall of the exhaust pipe becomes pronounced especially at the time of initiation of work by the construction machine, because the exhaust pipe has not been warmed up yet at that time.
Even when the above-mentioned after-treatment device is provided, soot and the like contained in exhaust gas cannot be treated completely. Soot and the like, therefore, adhere to the inner wall of the exhaust pipe when the exhaust gas guided from the after-treatment device is released to the outside. As a consequence, soot and the like accumulate on the inner wall of the exhaust pipe so that water droplets condensed and adhered on the inner wall of the exhaust pipe contain lots of soot and the like and have been blackened.
Accordingly, a conventional exhaust assembly for a construction machine, said conventional exhaust assembly being provided with such an after-treatment device, involves a problem in that water droplets condensed and adhered on an inner wall of an exhaust pipe and blackened there are forced out by exhaust gas guided from an outlet port of the after-treatment device, accumulate at an outlet of the exhaust pipe, scatter to the outside of the exhaust pipe, and hence, foul a body cover of a revolving upperstructure.
As one of conventional technologies for preventing the above-described problem, a muffler assembly has been proposed for a vehicle. This muffler assembly for the vehicle is provided on an inner wall of an exhaust pipe with a water-droplets capturing member. This water-droplets capturing member has a water-droplets intercepting ring inwardly extending in an annular form from the exhaust pipe and a ring-shaped flange extending in an annular form from an inner circumferential edge of the water-droplets intercepting ring toward a basal end of the exhaust pipe (see, for example, JP-A-2008-261242).
In the muffler assembly disclosed in JP-A-2008-261242, however, the water-droplets intercepting ring and ring-shaped flange of the water-droplets intercepting member extend inwardly and substantially in the annular forms at the outlet of the exhaust pipe as mentioned above. The opening area at the outlet of the exhaust pipe is, therefore, smaller than the cross-section of a passage for exhaust gas that flows through the exhaust pipe. Accordingly, the emission of the exhaust gas is interfered by the water-droplets intercepting ring and ring-shaped flange, the exhaust gas stagnates at the outlet of the exhaust pipe, and the exhaust resistance in the exhaust pipe increases. As a result, the acceleration performance of the engine and the fuel economy may be adversely affected. As water droplets are captured only at the outlet of the exhaust pipe, there is also a possibility that some of water droplets may be discharged to the outside.